Cyclic peptides

ABSTRACT

Cyclic peptides, such as 1,4,8,11-tetraazacyclotetradecane-5,12-dione, that are useful chelation agents for metals are prepared by contacting an acrylic acid ester and a 1,2-alkylenediamine.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional, of application Ser. No. 348,528, filed Feb. 12,1982.

BACKGROUND OF THE INVENTION

The present invention relates to cyclic peptide compounds also referredto as macrocyclic polypeptides. In particular, the present inventionrelates to cyclic peptides containing alanine moieties. The inventionfurther relates to a process for making the novel cyclic peptides of theinvention.

Numerous cyclic peptide compounds are known or have been described inthe art. Previously however, the synthetic methods employed have beentedious and complicated requiring the use of expensive reactants andsuffering from low yields of the desired cyclic peptide product.

Examples of known cyclic peptides include L-Pro¹ -tentoxin disclosed byD. Rich et al., J.A.C.S., 100, 2212 (1978). The compound was prepared bystandard blocking and deblocking techniques followed by intramolecularcyclization in pyridine solvent.

It is also known to cyclo oligomerize N-alkyl aziridines with variouscationic initiators such as BF₃ or paratoluene sulfonic acid to givetetraazacyclodecanes; see, e.g., S. Tsuboyama et al., Tet. Lett., 16,1367-1370 (1970); G. R. Hansen et al., J. Heterocyclic Chem., 5, 305(1968).

In U.S. Pat. No. 3,305,493, linear polymers of an acrylic acid ester anda polyalkylenepolyamine are disclosed. The linear polymers were formedby heating a Michael addition product of the acrylic acid ester and thepolyalkylenepolyamine to a temperature of from about 90° C. to about130° C. A similar process is disclosed by U.S. Pat. No. 3,445,441.

SUMMARY OF THE INVENTION

According to the present invention are provided novel cyclic peptidecompositions corresponding to the formula

    --NHCRHCRHNHCH.sub.2 CR'HC(O)--.sub.2                      (I)

wherein R and R' indepenently each occurrence are hydrogen or C₁₋₄alkyl.

Further included in the invention is a novel process for preparing theinvented cyclic peptide compositions comprising contacting an ester ofacrylic acid or an ester of a substituted acrylic acid with a1,2-alkylenediamine under conditions conductive to the formation of aMichael addition product and subsequently subjecting the Michaeladdition product to conditions conductive to the intermolecular andintramolecular amidation thereby forming the linear dimeric reactionproduct and cyclic peptide respectively.

The invented compounds are useful in forming chelates with metal ionssuch as copper, iron or zinc ions thereby aiding in solubilizing suchmetals in various systems. The compounds furthermore have been found topossess useful insecticidal properties.

DETAILED DESCRIPTION OF THE INVENTION

The invented cyclic peptides of previously described formula (I) areeasily prepared by reaction of an acrylic ester and a1,2-alkylenediamine. Suitable acrylic esters are those of the formulaCH₂ ═CR'CO₂ R" wherein R" is a C₁₋₈ normal alkyl radical, and R' is aspreviously defined. Examples include methyl acrylate, ethyl acrylate,n-butyl arcylate, methyl methacrylate, ethyl methacrylate, n-octyl ethylacrylate, etc. Preferred esters are methyl acrylate, ethyl acrylate,methyl methacrylate and ethyl methacrylate. A most preferred reactant ismethyl acrylate.

The 1,2-alkylenediamines are those of the formula NH₂ CRHCRHNH₂ whereinR is a previously defined. Examples include ethylenediamine,1,2-propylenediamine, 2,3-butylenediamine, etc. A preferred reactant isethylenediamine.

The Michael addition reaction is easily effected by merely contactingthe two reactants, preferably without a solvent, at a temperature fromabout -10° C. to about 80° C. Temperatures in excess of 80° C. tend tolead to production of longer chain linear oligomers instead of thedesired cyclic compounds. Preferred reaction temperatures are from about20° C. to about 60° C.

The ratio of ester to diamine reactants is from about 1:1 to about 1:7.Generally, excess diamine is removed by vacuum distillation followingcomplete addition of ester reactant to prevent formation of additionalamine adducts. A solvent is not normally required but may be employed ifdesired.

The Michael addition product,

    NH.sub.2 CRHCRHNHCH.sub.2 CR'HCO.sub.2 R",

readily undergoes subsequent intermolecular and intramolecular amidationreactions to form first the linear dimeric reaction product,

    H--NHCRHCRHNHCH.sub.2 CR'HC(O)--.sub.2 OR",

and then the cyclic polypeptide product,

    --NHCRHCRHNHCH.sub.2 CR'HC(O)--.sub.2.

It is only required that the Michael addition product be retained at atemperature of from about 10° C. to about 60° C. for a time sufficientto allow the elimination of two equivalents of the hydroxyl compound tooccur. Reaction times of up to several weeks may be required for thecyclization process to occur. Removal of the hydroxyl by-product, as byvacuum distillation, and purification of the product, as byrecrystallization from alcohol, may be employed if desired.

Alternatively, the Michael addition product may be dissolved in anaqueous solution for the cyclization reaction. Normally, the cyclicpeptide product, being less soluble than the addition product, isreadily precipitated from the reaction medium as it forms and isrecovered by filtration or other suitable means.

Heating of the addition product is generally detrimental to theformation of cyclic peptides and results instead in linear oligomerformation.

SPECIFIC EMBODIMENTS

Having described the invention the following examples are provided asfurther illustrative and are not to be construed as limiting.

EXAMPLE 1 1,4,8,11-Tetraazacyclotetradecane-5,12-dione

Methyl acrylate (344 g, 4.0 moles) was added dropwise into neatethylenediamine (240 g, 4.0 moles) while stirring. Addition wasconducted at such a rate that the reaction temperature did not exceed45° C. Addition time was 4.0 hours. The crude colorless product,N-(2-aminoethyl)-β-alanine methyl ester (580 g), was dissolved indeionized water to give a concentration of about 25 weight percent.Allowing the solution to stand at room temperature for 2-3 days caused awhite solid product to slowly precipitate. The product was obtained as afine white powder, m.p. 198° C.-199° C. Spectral analysis confirmed theproduct's structure as

    --NHCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 C(O)--.sub.2

EXAMPLE 2

The reaction condtions of Example 1 were substantially repeatedexcepting that the ester reactant was ethyl acrylate. Accordingly, ethylacrylate (100 g, 1.0 mole) was added dropwise into neat ethylenediamine(60 g, 1.0 mole) while stirring. The reaction temperature was notallowed to exceed 55° C. and was completed over a period of 1.25 hours.The colorless, slightly sweet smelling liquid product weighed 160 g (100percent yield). Distillation of this product gave a major fractionboiling at 180° C.-143° C./2 mm, weight 42.4 g which was identified asN-(2-aminoethyl)-β-alanine ethyl ester. Allowing this fraction to standat room temperature caused it to transform to a white, slushy,semi-solid which weighed 4.05 g (9.56 percent) after filtration.Recrystallization from hot ethanol gave 1.25 g of fine fluffy whitepowder, m.p. 192° C.-193° C. which was spectroscopically identical tothe product obtained in Example 1.

EXAMPLE 3 6,13-Dimethyl- 1,4,8,11-tetraazacyclotetradecane-5,12-dione

Ethylenediamine (240 g, 4.0 moles) was placed in a 1000-ml 3-neckround-bottom flask equipped with air stirrer, addition funnel and refluxcondenser. Methyl methacrylate (400 g, 4.0 moles) was added at roomtemperature over a 1-hour period. The product, a mixture ofN-(2-aminoethyl)-α-methyl-β-alanine methyl ester and methanol, wasallowed to sit at room temperature for 2 weeks during which time a whitecrystalline precipitate formed.

The precipitate was isolated by filtration and recrystallized fromethanol. The compound melted with decomposition at 260° C.-261° C.Elemental analysis yielded C-56.1 percent, H-9.32 percent, and N-21.8percent. This compares well with the theoretical ratio of56.22:9.44:21.86 for the macrocyclic dimer. The mass as determined bychemical ionization mass spectroscopy was 256 as further confirmation ofthe structure.

What is claimed is:
 1. A process for preparing a cyclic peptidecorresponding to the formula

    --NHCRHCRHNHCH.sub.2 CR'HC(O)--.sub.2

comprising contacting an acrylic ester of the formula CH₂ ═CR'CO₂ R"with a 1,2-alkylenediamine of the formula NH₂ CRHCRHNH₂ wherein R and R'are independently each occurrence hydrogen or C₁₋₄ alkyl, and R" is C₁₋₈alkyl under reaction conditions conductive to the formation of a Michaeladdition product and thereafter subjecting the Michael addition productto a temperature between about 10° C. and about 60° C. for a timesufficient to form the cyclic peptide.
 2. The process of claim 1 whereinthe acrylic ester is contacted with the 1,2-alkylenediamine at atemperature from about -10° C. to about 80° C. in the absence of asolvent.
 3. The process of claim 2 wherein the temperature is from about20° C. to about 60° C.
 4. The process of claim 1 wherein the Michaeladdition product is subjected to a temperature of from about 10° C. toabout 60° C. for a time up to about several weeks.
 5. The process ofclaim 1 wherein the acrylic ester is methyl acrylate, ethyl acrylate,methyl methacrylate or ethyl methacrylate and the 1,2-alkylenediamine isethylenediamine.